Electrostatic sound reproducer



1950 J. w. AcosTA 2,519,810

ELECTROSTATIC SOUND REPRODUCER Filed Dec. 5, 1947 HAT-5 0F 007, 07 TUBE JNVENTOR. JOSE W. 400.9734,

A rr'omvzvs.

Patented Aug. 22, 1950 UNIT ED ST PAT E NT OF F l C E ELECTROSTATIC ISOUN D REPRODUCER Jos: W; Acosta, Ghicago,- Ill.

Application-December 5, 1947; Serial' Noi 790,001

Claims, 1 This: invention relates-- to sound. reproducers} and: more particularly to. loud. speakersion use with-electron tube amplifiers.

A main object of the invention isyto-providea novel and improved sound reproducer' for use withelectron tube audio amplifiers said reprorducen roviding improved tone.- quality; without the: need for elaborate bafliing. of. therreproducer diaphragm unit and also providingan impedance substantially matching the impedance oft-the output tube of the amplifier.

Aiurther object of the. invention. is to. provide: an improved electromagneticysound repro; duccrt which is relatively simple in construction, which provides tone, quality wherein. the low audio; frequencies are reinforced, and. which; is substantially non-directional.

Eurther objects and. advantagesof the inventtion w-illlbecome apparent from the following; de-

scription; and claims, and fromthe2accompanying drawings, wherein:

Figure 1 is: alongitudinal cross-sectional view takenzthrough a loud speaker constructed in ac:- cordance-with the present invention.

Figure 2;- isa perspective view'of assimplifled form; of loud speaker according to the present invention.

Figure 3. is a bottom diagrammatic view illustrating; a modification of. the; loud speaker of figure- 2'.

Figuredv is anelevational view of aloud speaker constructed in accordance with Figure? Figure. 5,-is a longitudinal crossr-sectionalview illustrating a further modification of: the: loud speaker of Figure 1.

Figurefi is a schematic diagram illustrating-the equivalent circuit. of. the loud speaker deviceof Figure 1.

Referring to the drawings, and more particularlyto Figure l, i l designates a permanent magnet, said magnet being preferably cylindrical and having axially-secured theretoxatt'one end a nonmetallic stud l2. Wound on the magnet Has a core is a coil l'3 having a large number of turns, the lead wires of said coil being shown respectively at-I4 and l'5. Surrounding coil i3 is a cylindrical iron shell It w-hichis not permanently magnetized-but which has-a relatively high:per-

-meability-to magnetic flux. Wound 0112511811 I6 another" coil I? having relatively few turns, the leadz-wires of coil llbeing'shown respectively at l8-:and l9. Surroundingl'coil His a thin' metal shellzfl of ametal foil or the like.

Slidably mounted on the stud I2 is a'cylindricap member 2| of insulating material; and axially secured to the endwall thereoflisarod member. 22 connected to. the apex of a conventional speaker cone 23. Wound. on capzmember ll; 1523' voice coil 24 comprisinga few turns of put .tube'nf the audimamplifien CoilI terminal i5: is: cormectedi to. a wire 2.11 which in turn' is connectedtotheplate of" said output tube. The. terminal I3- of.outer:coil |..l is-connectedto-wire12'1f. Theother, terminal 19' of said outer'coil is: con;- nectedto ground through aresistor iai Itwill beinotedzthatouter: coil I! isininductivesrelation with inner coil, [Sand may beconsideredwas the lowfvoltage-s portion of an auto-transformer winding.

One end-of inner shell, I this connectedzby. azwire 29;through: a condenser-3B. to the plate wirexzll The-outer diaphragm'shell 2i is-connectedrto the voicecoil wires25 Terminal wire 2.6:of thervoice coilisconnected to ground through. aresistortd:

In-operation; audio: currents; flow to voice: coil 24* through: a circuit. comprising wire. 27', con:- denser: 39; ,wire .29, the; capacitance between inner shell f6 and outer: shell 20,,wire 25, voice coil; 24'; wire 25'; resistor-33 and the ground returnrsysytem; of. the output tube. Plate; current: flows through coil I3 since saidcoilfisconnecteddi; rectly, in", they plate circuit of the output tube: $111681 coil I3- is inductively coupled to: coilv l1; audio currents also fiowrirrcoil L1 Sil'lCB'COil: l1- isizin-l capacitive relationshiprtooutershell 2ll,xthe audioxsignalcarried by coil H is couple-diintocthe circuit of voice coil. 24 by. thevcapa'cityr existing between the turns of 'coilll Tand'theoutershell 2'0.

The m'agneti-zing-:force of coil l3z-acts through the core l-I. to; move; the voice coil. and. the cap member 2 l on-which it is mounted axially-in re;- sponse to the audio current. fluctuations in the plate" circuit; of: the. output tube; the; amplitude of movement of the, voice coil being reinforced by the interactiombetween the-magnetizing force producedibythe audio currents, in. the .voice I coil andthe magnetizing forceaproduced by the audio currentsin coil I3.-

The; condensertfl'; compensates for the phase shift produced by the coupling cap-acitancebetween. shell .lfi-gand shellzfi. The phase shift produced by the-coupling capacitance between the turns of.:outer.- coil" I'I'and shell Zllfis balanced out by-the inductive phase shift caused by. the direct OOHIIBCfiOHzOfz coil. l1 between; thesplatev and". the ground-return'path of the outputtube.

Coil 24- is wound so'that itsrmagnetizingiorce opposesthe magnetizing force-of coil 13. A. suit:- able springz24 may beinterposed:betweenv cap member 2| and the speaker frame" to. bias'said cap'member to anormal axialposition. Audio current. fluctuations inthe plate circuit: of. the output tube will. therefore drive cone 23* axially against-:the biasing force of said spring.

The values of resistors 28 and 33 are preferably soochosen asrto provide animpedancematch of the-reproducer to the impedancev of the output tube; whereby maximum. output-efficiency: of the tubeiswobtained.

ItvWill' bernoted thattheDaC. componentzof the plate current flowing in coil l3 functions tOfIBi'IIP force the; magnetizing forceof.- the: permanent magnet H and to thereby increase the maximum available undistorted output power of the reproducer.

In the embodiment of the invention shown in Figure 2, 34 designates a perforated metal shell employed as a core. Wound on shell 34 is a coil 35 of many turns having terminal wires 36 and 37. Wire 31 is grounded through a resistor 38. Designated at 39 is a wire connected to the plate of the output tube of an amplifier. Shell 34 is connected to wire 39 through a condenser 40.

Surrounding coil 35 and fitting thereon in a manner enabling it to vibrate, as for example, engaging the coil 35 with local frictional contact, is a shell 4| of light metal foil or the like. Shell 4| is connected to ground by a wire 42. It will be noted that shell 4! is electrostatically coupled to shell 34 and audio currents may flow through a circuit comprising wire 39, condenser 45, the electrostatic coupling between shell 34 and shell 4|, wire 42 and the ground return system of the output tube. Shell 45 vibrates in response to the audio currents flowing through the capacity between said shell 4| and the shell 34, localized free portions of the shell being driven by capacitive attraction, and may be utilized as an independent sound reproducer. Shell 4! is also electrostatically coupled to coil 35, and shell 4| is also driven to some degree by the capacitive attraction between the shell and the distributed turns of the coil. The condenser 40, in series with shell 34, provides a phase correction in the circuit including the electrostatic coupling between shell 34 and shell 4|, which causes the shell 4| to be driven substantially in phase by the electrostatic coupling'between shell 4| and shell 34 and the electrostatic coupling between shell 4| and coil 35.

In the embodiment of Figures 3 and 4 the outer sheath which is in electrostatic coupling relation with either the inner shell I6 of the embodiment of Figure 1, or the shell 34 of the embodiment of Figure 2, is divided into a plurality of vibratory segments, shown in die, 4|b, M0 and Md, and connected to each segment is a speaker cone 43. The segments are preferably equally spaced around the axis of the unit so that sound may be radiated from said unit with equal intensity in all directions. Although four segments are shown in Figures 3 and 4, obviously any desired number of segments may be employed, each segment being of course connected to a separate speaker cone. In the embodiment specifically illustrated in Figures 3 and 4, the voice coil of Figure 1 and cone 23 of said figure are eliminated and the unit is mounted so that the speaker cones 43 extend horizontally. The segments 4m to 4|d are preferably dimensioned so as to have substantially equal response over the entire range of audible frequencies since they are employed as independent reproducers. Suitable lead wires 45 are provided for each segment for connecting the segments to the ground return system of the amplifier output tube.

A flanged top cover 44 may be mounted on the unit, as shown in Figures 3 and 4, said top cover acting to mufile the sound produced by the segments 4|a to 4 Id so that it will not interfere with :sheath.

While certain specific embodiments of sound 4 reproducers in accordance with my invention have been disclosed in the foregoing description, it will be understood that various modifications within the spirit of said invention may occur to those skilled in the art. Therefore it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims.

What is claimed is:

1. A sound reproducer comprising a metallic core, an audio input coil wound on said core, a plurality of vibratory members spaced around said core and electrostaticall coupled therewith, and circuit means for connecting said input coil and the capacitances comprising said vibratory members and core to the output terminals of an audio amplifier.

- 2. A sound reproducer comprising a coil, vibratory means electrostatically coupled to said coil, circuit means connecting said coil and vibratory 'means to the output treminals of an audio amplifier, a metal core within said coil, and a condenser connected between said core and one of said output terminals.

3. A sound reproducer comprising a core a coil wound around said core, vibratory means electrostatically coupled to said coil and responding to the fluctuations of current flowing through the capacitance between said vibratory means and said coil, circuit means connecting said coil to the output terminals of an audio amplifier, means connecting said vibratory means to one of said output terminals and a condenser connected between said core and the other output terminal.

4. A sound reproducer comprising a hollow metallic core, a coil Wound on said core, a thin vibratory sheath electrostatically coupled to said coil and also electrostatically coupled to said core, circuit means connecting said coil to the output terminals of an audio amplifier, and additional circuit means respectivel connecting the core and sheath to the respective output terminals.

5. A sound reproducer comprising a hollow metallic core having perforated end walls, a coil wound on said core, a thin vibratory metallic sheath on said coil and electrostaticall coupled thereto and to said core, circuit means connecting said coil to the output terminals of an audio amplifier, and additional circuit means respectively connecting the core and sheath to the respective output terminals.

Josii W. ACOSTA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,183,404 Rummler May 16, 1916 1,656,514 Fay et a1. Jan. 17, 1928 1,672,173 Rowe June 5, 1928 1,689,564 Thorington Oct. 30, 1928 1,707,713 Dieterich Apr. 2, 1929 1,732,427 Andrews Oct. 22, 1929 1,753,137 Seibt Apr. 1, 1930 1,754,928 Albertus Apr. 15, 1930 1,774,855 Titcomb Sept. 2, 1930 1,889,748 Gruschke Dec. 6, 1932 1,983,377 Kellogg Dec. 4, 1934 2,078,469 Thomas Apr. 27, 1937 2,353,162 Kaltenbacher July 11, 1944 2,416,557 Wiener Feb. 25, 1947 1 2,422,707 Turner June 24, 1947 

